4）MRIからみた直腸癌の深達度診断

Tumor Staging of Rectal Cancer by MR Imaging

要旨　近年の直腸癌に対する治療法の進歩は，正確な腫瘍の解剖学的位置と深達度診断を必要としている．直腸内コイルを用いたMR画像は，T2強調像にて正常の腸管壁を表層の粘液および腸管周囲の脂肪織を含めて5～6層に分けて描出でき，粘膜層は低信号，粘膜下層は高信号，固有筋層は低信号を示した．したがって，腫瘍の壁内浸潤の診断が可能であり，特に粘膜下層に予め生食水を局注することによりm癌，sm癌とmp癌との鑑別の成績が向上した．また，MR画像は，腫瘍のわずかな壁外浸潤の診断能にも優れており，T2強調像では低信号を示す外縦筋層の断裂として描出された．直腸内コイルを用いたMR画像は，直腸癌の治療法の選択において重要な情報を提供できると考えられた．

　Our purpose was to evaluate the visualization of the normal rectal wall, the accuracy of local staging of rectal cancer and lymphnode metastasis by MR imaging, for the planning of treatment. Fifty-five patients with rectal cancer were examined by endorectal MR imaging. The depth of carcinomatous invasion and the presence of lymphnode metastasis were diagnosed before resection. To make the submucosa thicker, we endoscopically injected saline into the submucosa under the tumor in eleven cases. The normal rectal wall was visualized as a five-to-six-layer structure including superficial mucus and perirectal fat tissue on T2-weighted images. In 45 out of 55 cases (81.8%),MR images led to a correct diagnosis of the extent of tumor infiltration. The technique of submucosal saline injection helped to assess the differentiation between non or minute submucosal invasion (m- or sm₁-carcinoma) and massive submucosal invasion (sm_2,3-carcinoma).

　Endorectal MR imaging can detect intramural tumor infiltration with all the layers of the intestinal wall depicted. Our results suggest that endorectal MR imaging can improve the accuracy of tumor staging and provide information leading to the most suitable surgical therapy for rectal cancer.